Thursday, February 12, 2015

A messed up surrogacy

By: Paul Cavalho

Imagine a mama bear grabbing you and shoving its fertilized
egg inside you. The baby bear starts to develop and slowly eat you from the
inside until you give birth. Although it might look cute, you probably want to
kill it for what is has done to you. Just when you think this traumatic
experience is over, you immediately get a virus and now you’re paralyzed. Your
feet are planted over this bear cub, protecting it from other creatures that
attempt to prey on it. Finally, the cub can fend for itself and waltzes off
without a thank you. You are free at last.

Wow what a horrific thought…unless you’re Chuck Norris, then
of course you would be shoving your baby inside the bear. On a serious note, welcome
to the trials and tribulations of the spotted lady beetle, lady bird or ladybug
whichever you prefer.

Female wasps deposit their eggs inside the ladybug through
an organ called an ovipositor. A single wasp larva will develop inside a
ladybug over the course of 20 days, feeding on nutrients inside the host. Just
after this larval development period, the larva becomes a prepupa which will
exit via the segmented abdomen of the ladybug. The prepupa spins a cocoon
between the ladybugs legs and the ladybug exhibits a change in behavior. That’s
right…the ladybug is still alive, but seems to be almost paralyzed. The ladybug
grasps the cocoon but still displays random movements, especially when it’s
disturbed. This is known as bodyguard manipulation.

The most amazing part of this behavioral manipulation is
that the ladybug no longer has the parasitoid wasp inside its body. Also, the
effects are strangely timed with that of the adult wasp breaking out of the
cocoon. Once the adult wasp flies away, some ladybugs fully recover and even go
on to reproduce – more little ladybugs, not more parasitoid wasps.

Other species of parasitoid wasps have been known to use
polydnaviruses – viruses which the whole virus genome is embedded within the
wasp’s genome. Polydnaviruses are usually injected into the host simultaneously
with the eggs, and affect the host’s immune system immediately. This type of
virus appears to be absent from the D.
coccinellae genome!

So how are these wasps manipulating their hosts?

A group of scientists observing this phenomenondiscovered a new type of virus inside
the head region of parasitized ladybugs; they named it Dinocampus coccinellae paralysis virus (DcPV). The researchers
hypothesized that DcPV is associated with Dinocampus
coccinellae and infects the nervous system of the ladybugs, contributing to
behavioral manipulation after the prepupa emerges from the ladybugs abdomen.

The researchers found DcPV in all adult wasps and larvae
tested, but this virus’s genome was not embedded within the D. coccinellae genome. This information
suggests DcPV is living inside the wasp symbiotically. Electron microscopy of
cells in wasp ovaries and oviducts revealed small compartments or vesicles
inside cells housing the virus in a very orderly fashion as seen below. They
also found that the adult wasps harbored more non-replicating forms of the
virus, but replicating DcPV was more prevalent in larva that was cut out of
ladybugs during parasitism.

Ladybugs were exposed to parasitism by D. coccinellae in a lab setting, and
the heads and abdomens were sampled at 5, 13 and 20 days after the wasp
deposited its eggs. At 20 days after, just before prepupa crawl out of the
ladybugs , DcPV levels were much higher than at 5 and 13 days after, suggesting
DcPV plays a role in manipulating host behavior.

The results from these studies suggest DcPV is associated with
D. coccinellae and plays an important
role in bodyguard manipulation, but researchers say there is much more research
to be completed before a definitive conclusion can be made about the role of DcPV.

And now I will apologize for putting that initial image in
your head, I hope you can recover.